From practical experience, bearing devices are known in which a bearing supports a shaft so that it can rotate, wherein the bearing device has a safety bearing that holds the shaft if the bearing fails, so that the shaft can run down in the safety bearing. The bearing ring of the safety bearing facing the shaft has, during normal operation of the bearing device, a distance to the shaft and is mechanically unloaded. If the safety bearing is constructed as an anti-friction bearing or if the safety bearing comprises at least one anti-friction bearing, the row of these anti-friction bearings is not or only slightly mechanically pre-tensioned by an additional spring means. For example, bearing devices are known with a magnetic bearing and a safety bearing that holds the shaft supported in the magnetic bearing if there is a loss of power.
If the shaft enters into the safety bearing, high forces and accelerations occur. In particular, if the safety bearing is made from anti-friction bearings and comprises at least one row of anti-friction bodies, there is the risk that the safety bearing will fail on the short term, because the anti-friction bodies are subject to high initial acceleration and slippage occurs due to the lack or only slight mechanical pre-tensioning of the anti-friction bodies. This slippage is associated with damage both to the anti-friction bodies and also of the bearing rings of the safety bearing, so that the safety bearing must be replaced often after only one use.
In practice, the case often occurs that the shaft acts on the bearing ring at an angle with respect to the rotational axis of this bearing ring of the safety bearing facing the shaft. Likewise the case occurs that the shaft is not only tilted with respect to this rotational axis, but also enters the safety bearing with a bent shape. A reason for this can be the time offset release of the shaft in the bearing or the failure of only one sub-bearing of several sub-bearings of the bearing. Due to the tilting or bending of the shaft, a section of the bearing ring of the safety bearing holding the shaft is subject to a high application of a force, while a different section of this bearing ring is subject to only a small application of force. Especially in a safety bearing formed as a multi-row anti-friction bearing, one row of anti-friction bodies is subject to a strong loading that leads to slippage, while the other row of anti-friction bodies is subject to no loading. If the safety bearing comprises two adjacent anti-friction bearings that contact each other, one of the two anti-friction bearings is loaded strongly and the other only slightly. In both cases, there is strong wear in the safety bearing that might need to be replaced after only one use.
DE 602 09 752 T2 describes a bearing device with a magnetic bearing and also a safety bearing, wherein the safety bearing comprises two axially adjacent, mutually contacting, mechanically pre-tensioned angular contact ball bearings. The two-piece lateral surface of the two-piece bearing ring of the safety bearing facing the shaft has, close to the end faces, a cylindrical form up to an edge rounding that is typical in anti-friction bearings and has a straight contour pointing parallel to the rotational axis of the two angular contact ball bearings. If the shaft enters into the safety bearing tilted or bent with respect to the rotational axis, the two angular contact ball bearings are loaded unequally, wherein especially strong slippage occurs in one of the two angular contact ball bearings. The safety bearing therefore has only a shortened service life.
DE 197 29 450 C2 describes a bearing device for supporting a rotor so that it can rotate in a bearing, wherein two anti-friction bearings formed as a single-row ball bearing are provided as a safety bearing. Each bearing ring of the safety bearing facing the rotor shaft has a cylindrical lateral surface up to the typical edge rounding at the transition to the end face with an essentially straight contour running parallel to the rotational axis of the bearing ring. If the shaft enters tilted or bent into one of the two ball bearings, the ball bearing is loaded unequally and its service life is significantly shortened.